text:
Why does the Neutral Point not vary with Tail incidence angle?
The neutral point is the position where if the CG were present, the aircraft would be statically neutral, ie., the moment about the CG would be constant with varying AoA.
Now, consider an aircraft with a wing and tail only. In this case, the moment generating sources would be the wing lift, wing moment about its AC, tail lift, and tail moment about its AC. We know that both the AC moments will be constant with AoA, so it will only be the lifts that vary with AoA. Thus for the aircraft to be neutral the moments at the neutral point from the lifts of the tail and wing would have to cancel out.
Now, if we change the angle of incidence of the tail, the tail lift would change over the whole range of aircraft AoA (not just one AoA value) thus requiring the neutral point to shift so that the lift from the wing can continue to be cancelled out.
I know how in the equations the angle of tail incidence doesn't factor in in the neutral point or Cm slope equations, but I am unable to intuitively understand the fact, as you can see.

Well, in practical terms I've found that with some radio-controlled model sailplanes, it seems that the stability does vary with the tail incidence angle.  At my current CG, my "Radian" r.c. sailplane is positively pitch stable enough to recover from mild disturbances when trimmed for low-speed flight, but when trimmed for high-speed flight, the least disturbance leads to a very steep dive.  (And naturally, the trim position for high-speed flight involves a lower elevator position than for low-speed flight, and a lower el. position is like a less pos. or more neg tail incidence angle.)

(Likely many confounding factors here but... )

All your reasoning is perfect until here:

Now, if we change the angle of incidence of the tail, the tail lift would change thus requiring the neutral point to shift so that the lift from the wing can continue to be cancelled out.

There you've forgotten that what is important for the stability is not the lift itself rather the change of lift with AoA i.e. the slope of $C_L$. This is exactly why you've correctly written that the wing's and tail's moment don't enter in the stability calculation since

both the AC moments will be constant with AoA

and their contribution to the stability is zero (they're constant i.e. their change with AoA is zero).
The slope of $C_L$ is basically constant for all the AoAs of interest and therefore neither the neutral point nor the stability characteristics of the airplane change with tail setting (but the trim does).

Understood, Thanks!

requiring the neutral point to shift so the wing can continue to be canceled out.

Remember, the tail controls pitch.  Incidence change is is exactly what one does with an "all moving surface", such as a stabilator.  Tail trim is used to cancel out all other torques around the center of gravity for a stable pitch to the horizon.
Neutral point is based on the longitudinal stability of the aircraft.  If one made the tail area smaller, or with a lower coefficient of lift, the neutral point would move forward.
This is why delta designs became more popular when (jet) engines were placed more to the rear.


text:
What altitude to use for IFR off-airways route
Say I want to fly off-airways (both Victor airways and T routes) for my IFR flight, direct to my destination in the US.  How do I know what my off-route altitude should be so I can file for that?
I would expect this would be an altitude above the OROCA and suitable for direction of flight, however I encountered this in the Instrument Procedures Handbook:

OROCAs are intended primarily as a pilot tool for emergencies and
SA. OROCAs depicted on en route charts do not provide the pilot
with an acceptable altitude for terrain and obstruction clearance
for the purposes of off-route, random RNAV direct flights in either
controlled or uncontrolled airspace. OROCAs are not subject to the same
scrutiny as MEAs, minimum vectoring altitude (MVAs), MOCAs, and other
minimum IFR altitudes. Since they do not undergo the same obstruction
evaluation, airport airspace analysis procedures, or flight inspection, they
cannot provide the same level of confidence as the other minimum
IFR altitudes.

This suggests we cannot trust the OROCA.  Then I suppose the 14 CFR 91.177 indicates I need to be at least 2000 ft above the highest obstacle within 4nm of my course in mountainous areas, or 1000 in non-mountainous areas.  But how do I know what this is without using OROCAs?  Do we check sectional charts, or is there something more practical?  Checking a sectional seems reasonable on the ground for filing, but not so if diverting in the air and flying direct to some other airport on an off-airway course not planed on the ground.
Thanks for any help!

This article covers the topic quite nicely

To begin with, a direct route will only be approved in a radar
environment. In many areas of the country this is not an issue. The
pilot, however, must be aware that filing an altitude at or near the
OROCA (Off-Route Obstruction Clearance Altitude) may not guarantee
radar coverage. In that case, the pilot should expect to be assigned a
different altitude or route.

Its also covered in this AOPA article a bit

If you plan a "direct" flight, point-to-point, follow the rules and
enter the correct equipment. For example, if "/G" (or "slash Golf,"
meaning that your airplane is equipped with an IFR-approved GPS and a
Mode C transponder) or "/I" (you have loran or VOR/DME and a Mode C
transponder) are not entered for these kinds of flights, the air
traffic control computer will reject your flight plan because that
route can't be flown with less capable equipment. Direct routing
requests also are approved only in a radar environment, so forget
about filing direct, off-airways when radar is not available, or in
areas of poor radar coverage.

So broadly speaking you can file the OROCA but ATC may issue a higher altitude for radar coverage reasons. I have also received direct routings en-route at previously filed altitudes if they meet the requirements. Where I fly its common for ATC to prefer an airway route to get you out of the terminal area but will generally clear you direct once in route.

Thanks.  If you lose comms and thus can't benefit from radar coverage, what do you do?  Do you proceed direct still at your assigned altitude (don't have an MEA and MIA might change), and climb later if OROCA suggests it?

@Cameron that is a perfect question to ask on this site. Generally comments are not for extended discussion. Id be happy to answer/you will get a more verbose answer, if you post that.

Dave gave a very succinct answer to your question. I might add that in reference to your additional question regarding diverting to another airport, using an altitude above the OROCA or MORA for each successive grid you encounter would be your starting point.
If you have two-way communication with ATC, they will direct you to an altitude that provides the best chance at radar contact and NavAid reception. If you are not in two-way communication with ATC, a climb to a higher altitude would be in order as long as you stay well above the OROCA or MORA.
The OROCA and MORA are based on the charted terrain and obstructions. They do not take into account a temporary obstruction or uncharted item. Just remember, as the citation you quoted says, you will have to be aware of any airspaces (including airways, procedure routes, SUAs, etc), radar dead zones, NavAid dead zones, etc. Even terrain and obstacles clearance is not guaranteed due to the route not being flight inspected.
Here are two interesting articles on such:
From Jeppesen
From AOPA

source: Stack Exchange

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text:
Are there any remaining flying boat or seaplane airliners in operation?
Is there anywhere in the world that still offers scheduled air carrier service using flying boat / seaplane types of aircraft - something akin to a proper airliner? Or are they all limited to charters and shuttle-type flights on de Havilland Otters and the like?

What exactly would you consider a "proper airliner"? A Twin Otter can certainly be an airliner ("Currently, 38% are operated as regional airliners", Wikipedia). Trans Maldivian Airways for example only operates Twin Otters.

Maybe you should be asking if there are any operable flying boats in operation before asking about scheduled services.

I know for a fact that there are flying boats still operable. For example Grumman HU-16 was in use by the U.S. Coast Guard until the mid-80s and in the Greek Navy until the mid-90s. Many of these aircraft are still in private use today.

I understand that the term "airliner" can be vague. Perhaps a good follow up question would be: If there are airlines still operating on the water, what are some of the most significant in terms of passenger carrying capacity and/or distance of routes?

Hey, uh, maybe it's kinda late, but could you clarify whether you want to know specifically about flying boat or about all seaplanes in general? Your title says "flying boat", but in your question, you refer to using flying boat / seaplane Moreover, you go on to ask are they (seaplane operations) all limited to charter or shuttle-type flights on De Havilland Otters which could give the impression either that the Otter is a flying boat (it's not) or that your question is not limited to flying boats (but your title is?).

Coulson Flying Tankers effectively grounded the last Martin Mars water-bomber in 2018. They are fondly missed.

What about ground-effect vehicles? Are there any transport companies offering scheduled travels using these very-low-flying aircrafts?

As far as I know, there is no actual flying boat in use at an airline. The flying boats that are still in commercial operation are typically used for fighting forest fires or maritime patrol. This may change in the near future since there are currently at least two flying boats in development that might be used by airlines:

Dornier Seastar CD2: This is a newer model of the previous Seastar, which had its first flight earlier this year:

Dornier Seawings flew its new-generation Seastar amphibian for the first time on 28 March from its base in Oberpfaffenhofen, Germany.
[...]
Dornier says the aircraft will be offered in various configurations including cargo, passenger, special missions and VIP transport.

(flightglobal.com, emphasis mine)

AVIC AG600: This is new aircraft developed in China and one of the biggest flying boats ever. It had its first flight in 2017 and according to Wikipedia is expected to be delivered by 2022, possibly also in a passenger variant:

Further variants may be developed for maritime surveillance, resource detection, passenger and cargo transport.

If you are not just interested in pure flying boats, but also floatplanes, then there are many airlines world wide that operate these on regularly scheduled flights. One of the biggest is Trans Maldivian Airways operating various variants of the DHC-6 Twin Otter. They operate 55 seaplanes, which according to Wikipedia makes them the biggest seaplane airline:

TMA currently operates the world's largest seaplane fleet.

They offer flights to over 80 destinations:

Trans Maldivian Airways currently offers transfer services to more than 80 Maldives resorts, flying over 1 million passengers per year to their holiday hideaways.

(transmaldivian.com)
This is their main terminal at Velena International Airport:

(image source: Wikimedia)

Having flown TMA 3 times, I can say they're my favourite. Not the most comfortable, not the most luxurious but it means youre about to spend a week or 2 in pure luxury!

The AVIC AG600 Wikipedia article makes it sound as though the anticipated passengers may be troops on their way to the Spratly Islands in the South China Sea, rather than fare-paying members of the public.  That's pure speculation of course.

@rclocher3 Yes, I think at the moment it is primarily developed for the military. That's why I quoted "Further variants may be developed". If there is a market, they may use it for normal passengers as well, but maybe not...

I like the Dornier registration "D-ICKS" (D-X) as a nod to the Dornier DO-X.

@BrianDrummond haha, I hadn't noticed. What a wonderful registration :D

@Bianfable "We've been doing this for a while"

Last time I was there (fifteen or so years ago) there was a thriving commercial air passenger operation, including at least a couple scheduled flights (weekly, I believe, not daily), at the north end of Lake Washington (near Seattle), officially in either Bothell or Woodinville, Washington state (comments reminded me it's Kenmore Air, in Kenmore, WA).  There were no flying boats in service there, but there were Beavers and Otters on floats.
Beyond that, there are a number of tiny (one or two aircraft) airlines operating scheduled feeder service in Alaska and northern Canada that operate on floats, because lakes and rivers are much more common in the wilder parts of the sub-Arctic and Arctic than even grass or gravel airstrips.  As long as there's water to land on at both ends, such aircraft are good to go (and some have retractable gear, so they can land on concrete if necessary) -- and if you're starting from a village equidistant from Fairbanks and Nome, these are likely to be your only choices for local service.  The bulk of their revenue is likely from hunting and fishing charters, like any bush operation -- but many of them operate weekly or twice-weekly scheduled flights to a hub terminal.

There is an extensive scheduled service float network operating around the southern BC coast; Harbour Air, Sea Air, Vancouver Island Air, West Coast Air and others.They run VFR-only sched services, meaning scheduled trips that make the rounds whether there is anybody on board or not. There is a steady scheduled seaplane commuter flow between Vancouver harbour and Victoria (the capital) and Nanaimo on Van Island.There is so much traffic that Vancouver Harbour is the only water aerodrome I know of that is not part of a land airport, and has a PCZ with a Tower (atop a waterfront office building).

You are thinking of Kenmore Air, which is in Kenmore.

You beat me too it!  3 miles from my house...  They also fly wheeled Caravans out of BFI to the San Juan Islands.

@AzorAhai--hehim I think you're correct.  I used to drive past there occasionally, late in the day, when I was a Seattle cab driver.  "City" borders are a little nebulous in that part of King/Snohomish counties.

Haha, not to sound rude, but I am correct, I'm from Bothell. Neither Bothell nor Woodinville actually has any waterfront. But I can see why it would be confusing, they do just run into each other.

Harbour Air, based out of Vancouver, also has a thriving service, but doesn't fly to Kenmore Air Harbor, they fly to the "Seattle" dock in Lake Union (which Kenmore Air does as well).

@AzorAhai--hehim I've flown Kenmore out of Lake Union. Nice sightseeing ride around Seattle. Dodging boats during the takeoff run was also an interesting experience. - lol

There is at least one jet flying boat, the Beriev B-200, in production.
The Wikipedia article gives it a capacity of 72 passengers. I don't know how many (if any) are employed in an airliner role, though this variant has a "pressurised and air conditioned cabin allowing transportation of up to 72 passengers.
The passenger variant is the BE-210 shown here at beriev.com

Most seem to be employed as water carriers in a firefighting role; it was designed to skim the surface and scoop up water at close to takeoff speed.

Any airliners offering regular people or cargo transport using this aircraft? The question is about airliners that takes off or lands on water.

Four or five years ago or so, Pacific Coastal Airlines spun off its seaplane division as Wilderness Seaplanes, which flies scheduled service in a fleet of four Grumman Gooses in British Columbia.

Grumman Geese??

I wish you'd kept the spelling.

Not "air carrier service", but Viking Air acquired from Bombardier the type certificates and continues to produce the CL-215, CL-215T, CL-415 and CL-415EAF as an aerial firefighter, an amphibious aircraft.
Again, not "air carrier service" but a true flying boat, Coulson Flying Tankers effectively grounded the last Martin Mars water-bomber in 2018. They are fondly missed.
The following relates to "Float planes", rather than "flying boats or seaplanes" ...
Viking Air also hold the type certificate for the legendary De Havilland DHC-2 Beaver DHC-3 Otter and DHC-6 Twin Otter. A refreshed, next-gen specification Twin Otter - series 400 is now back in Production.
From their website,

With a fleet of 57 de Havilland Twin Otters, Trans Maldivian Airways
operates the largest seaplane operation in the world.

TMA is the airline referenced in @Bianfable 's answer.

NORDIC Seaplanes flies daily between the two largest Danish cities.

With flying boats or floats?

It appears they fly just one aircraft, and that is a Twin Otter floatplane (!=flying boat)

The title just asks about flying boats, but the question body also includes "seaplane." A Twin Otter isn't a flying boat, but it is a seaplane.

This post is an answer, albeit not a good one. The tool to deal with this is voting, not deletion.

@reirab I think we should ask the questioner to be more clear. I just realized I didn't understand what type of aircraft he wanted to know about - flying boat or all types of seaplane - or whether he even knew the difference between them.

Now it turns out that my flag seems to be unnecessary, as the question turned out to include floatplanes.

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text:
Why hasn’t the Wankel rotary engine seen more use in aircraft?
The Wankel rotary engine seems to have several advantages over traditional reciprocating cylinder-and-piston designs. In general, they have a much higher power-to-weight ratio, less vibration, and drastically reduced rate of catastrophic failure, among many other benefits. I can only find disadvantages related to emissions and fuel efficiency. So my question is, why hasn’t it seen more use in aviation even though it seems very well suited to this application?

Costs a lot to develop and certify an engine, and there's a very limited market.  FWIW, having owned a couple of rotary engine cars, I can say that fuel economy isn't all that bad when you're running at a steady, high RPM, as you would in an airplane or driving long distances on interstates, which I did when I owned mine.  They're horrible in stop & go driving, or around town, though.

"seems to have several advantages..." that statement is simply incorrect, unfortunately!

@Fattie please elaborate.

@AaronHolmes - my comment is superflous with the excellent answers: unfortunately no matter how "natty" an idea: the connection of the tip of the piston/rotor to the wall of the barrel/cylinder ... is inherently, fundamentally, problematic.  Sadly!

@Fattie Thank you, and bonus points for use of the word “natty”.

The wikipedia entry seems to cover several specific examples with citations. Posting as a comment as I haven't checked that it addresses the specific details in OPs question . https://en.wikipedia.org/wiki/Wankel_engine#Aircraft_engines

@Freiheit: Well, now I’m even more confused. The Wikipedia section on Wankel aircraft engine makes them seem like a perfect option.

see also https://mechanics.stackexchange.com/q/33484

I always thought the main barrier to Wankel engines on aircraft was cooling. They are water cooled engines and need significant airflow to stay within water temp limits.

They do not have drastically lower rates of failure than comparable piston engines. Their manifest unreliability in automotive applications is one reason they failed so badly in the marketplace. My college materials science TA owned one and had it rebuilt four times. His record for the shortest distance before failure on a zero-timed Mazda rotary engine was 150 miles.
The breakdown mode was failure of the apex seals at the tips of the rotor due to poor lubrication, leading to excessive wear and scoring and the complete destruction of the seals. According to my TA, Mazda went through more than six fundamental redesigns of the apex seal system but never could completely solve the basic problem.

That’s terrible. By any chance, do you recall what specific problems he was having with it? I’ve always heard that a Wankel could fail, but fail slowly - meaning it would suffer from reduced power output which gradually worsens - but that it was essentially immune to sudden, catastrophic failure in the way a reciprocating engine could seize up. It’s interesting that he had so many issues. Thanks for the answer.

@AaronHolmes my rotary RX-8 "failed suddenly" in that it just stopped turning due to the rotor heads - which is the usual failure mode of these engines. They consume oil and if you fail to top them up it destroys the rotor tips.

@Jamiec  That sounds like (a) a failure to provide proper maintenance (b) an issue specific to automotive engines, and their stop/start regime

@MikeBrockington absolutely right.

@Jamiec I know that many of these engines, like the Mazda variants feed oil directly into the chamber to provide lubrication and aid in creating a seal between the apexes. I’ve also heard that many people recommend mixing 2-stroke oil into the fuel to further increase the effectiveness. However, several modern manufacturers, such as AIE, claim to have solved the issues of oil consumption and excessive wear. Many of these engines are being used in UAVs.

Wankel engines have seen a bit of use in tiny racers and, more recently, in a few UAV applications.  I think in both cases the reliability tradeoff is probably justified by the inherent risk of those activities, but in most aviation it would not be a palatable sacrifice.

I owned a 1976 Cosmo for a while in the mid-80s.  13B engine, 4 barrel carburetor.  Failed emissions every year I owned it (due to oil injection, I think), got terrible mileage -- but it would cruise from gas station to gas station at 90 mph without any complaints after I had it rebuilt.  It's a brilliant aircraft engine, with a 3:1 reduction system -- propellers don't like 6500 rpm cruise...

Specifically, the Apex Seals would fail, leading to poor compression in the engine for one or more of the combustion chambers. Not always related to poor lubrication, since the engine was designed to self-lubricate the Apex Seals (which led to a deliberate burning of oil, a trademark of the rotary engine). Once compression was lost, just like in a piston engine, power creation ability declined dramatically. This problem was solved more-or-less in the later years of the RX-8, but nearly every single RX-8 (and RX-7) owner has a story or stories about replacement or rebuild of the engine.

My RX-8 was on it's fourth engine, all replaced under warranty by the factory. The rotary design excelled at high-rpm performance, and was happy to sit pegged out at 9000 RPM all day. Power band in the car version started around 6500 RPM. For an aviation version, I'm sure there'd be a gearbox involved since most propellers don't do well at 9,000 RPM. The lack of moving parts (only 3 in the entire engine) makes it incredibly reliable, besides the Apex Seal problem. With proper engine maintenance, you would detect slight loss of compression early, avoiding any problems.

Funny, but I had an RX-7 that was bulletproof. Mazda rotary racing cars were very reliable too. Perhaps you mistreated your car.

As another answer points out, the main problem is poor reliability.
In a  conventional piston engine, the sliding contact of the piston against the cylinder wall is mostly against relatively cool metal and is constantly lubricated by oil from underneath. The contact is often maintained tightly by piston rings, which have a natural outward spring.
In the Wankel type the sliding contact of the rotor tip seal against the chamber outer wall is frequently against much hotter metal from recent combustion and is difficult to lubricate. A separate spring mechanism is required to hold the seal closed against the firing pressure, so the whole thing is more complicated. The result is that the tip seals are extremely demanding and tend to wear out or crack.
I seem to recall that Norton reckoned to have solved the problems but their bikes and UAVs failed to gain significant business. I don't know if there were other issues affecting that.

Thanks for the response. It seems like some of the problems are more endemic to automotive driving, with constant, wide, rapid RPM changes and more frequent engine starts and stops without allowing the engine to properly heat up.

I think most answers on this question are fueled by lack of knowledge on rotaries, these engines do have inherent flaws relating to apex seals but 90% of their "unreliability" claims come from pure ignorant owners (at least in the automotive world) and a complete lack of understanding on how to maintain one. Most rx8's can do 100,000 kms before needing a rebuild, (average running time for that many kilometers is 2000 hours) so this is relatively in line with most overhaul windows (thanks google). And least us not forget the rotary engine won Le-mans in 1991 and apex sealing technology has come a long way since then. However to actually answer the question the real reason is due to the effort in getting the engine certified and the costs involved.

Wankel RCE is still in use today for Ultralight, Parapente, and other uses. Aixro, Wankel Supertec, Wankel GMBH, AIE.uk, are offering Wankel Rotary Engines for sale, research exists in India. John Deere, also Curtiss-Wright, developed a line of Wankel prototypes for Aviation, in several power ranges. The John Deere engine had an SFC around 240 gr/HP/hr, good enough, if you consider that it can work with low grade gasolines, heavy fuel versions of Wankel existed also.
Light weight, compactness, faults being not that total and catastrophic as in reciprocating engines, are Wankel advantages, a 2-Stroke engine, with sudden seizing, plus torsional vibration problems in shaft from engine to propeller killed the BD-5 and some pilots.

The Wankel engines were tried on BD-5's. They are not used because they are water-cooled engines, generate a lot more heat than 2-strokes and conventional 4-strokes, and it is incredibly difficult to fit the hardware for a required cooling system in such a small airframe, particularly during taxi. The aircraft simply wasn't designed to use such an engine. Torsional issues in the BD-5 drive system were resolved long ago. You just have to follow the plans and use the correct drive system from a knowledgeable manufacturer with a good track record.

Good observation. You know the NACA air intakes in BD-5 were tested, and resulted worse than 'Open mouth', the 'Vought F-8 Crusader' style. Small Wankel of today are also Liquid cooled (Aixro,...), but Air cooled Housing with Charge cooled Rotor versions existed. You may like 'Cooling your Wankel', by Paul Lamar, www.rotaryeng.net site, he proposed for Mazda conversions a Cooling similar to Mustang P-51, which added thrust from engine heat. Blessings +

What many BD5 builders never understood is that cooling an engine is not about how much air you bring into the engine compartment or onto the face of a radiator, it's about how much heat you take away. The only successful engine cooling designs for the BD-5 when using recip engines work by exiting the air through the bottom of the tail with vents cut out at the rear. The P-51 design was not very adaptable to the BD-5 because the bottom of the bird already sits very low to the ground, particularly with the pilot in the cockpit.

A Critique of the BD-5 Concept, Part 1 - PDFHALL.COM  in https://www.eaa.org/eaa/aircraft-building/kits-and-plans/00---c/bede-bd-5

That is not a critique, that's just the EAA info page on the BD-5. Most of it is accurate but there is some very dated information in it.

Sorry, I have no pilot license, I own no BD-5, I never built an airplane. If you read in full the link, you'll see an expert installed the P-51 Mustang Style of Cooling in the BD-5, with good results. About Wakel, this was the main question, you can access the www.aixro.de site, and have a look at the constant power Wankel they offer, at least one at 40 HP useful for UL aviation, and its weight with all accesories, including Cooling Radiator, Water,... Btw Propylen glycol is better than Ethylen glycol as antifreeze and cooling liquid, SAE papers 741091, 840237  I can't do more. Salut +

I am well aware of what work has been done on various BD-5's. That style of cooling air scoop has never been used with a Wankel engine on a BD-5 because the engine generates too much heat and it is simply too difficult to dissipate the heat in anything but normal cruise airspeed. "Installed" <> "Operating". Anybody can claim they installed anything, but the definition of success goes much further than just installing something. Like I said, the EAA page is not a critique. You want more info about the BD-5? Visit the BD-5 home page.

Dear mr Jilimenez: the EAA link includes an image of a BD-5 with P-51 style of radiator, also one with a supercritic profile propeller, if the original engine in BD-5 was a 2 stroke, prone to hacer perla: foul plug, and griparse: stuck, 36 HP, 27 kW, the Aixro engines will fit; you can have data of weight including cooling system in their site. To avoid overheating, any electric fan, thermostat controlled, will do the job. Is there any special reason you seem discussing so hardly my comments? I'm not in a power struggle, but trying to obtain and share information. OO R U?.  Agur. Blessings +

I'm not discussing anything, I am simply pointing out facts to someone who has never built a BD-5 and should not be making statements such as "any electric fan... will do the job." It simply doesn't work that way, sorry. The EAA link has only one picture, and it's BD-5J jet flown by Corkey Fornof.

As you point, Sport Aviation, Aug 1986, 'A critique of the BD-5 concept', by Seth B Anderson, included an image: 'P-51 Style Coolant Radiator on the author's BD-5', so it's possible adding a cooling howl under fuselage. About electric fans, it won't be difficult finding a radiator + fans, dimensions fitting your engine, thermostat controlled, it can even blow air from sides, allowing ram air in flight. From Sachs research on Small Wankel Engines, Keller, we know a blowing fan is better than a suction fan. Comment is generic about cooling motorcycles, karts,..Yes, I've never built. Blessings +

Placement of any type of fan, electric or belt controlled, in front of radiator has the logical advantage  that it works on cool air, while if placed behind radiator, as in most old cars, it will handle hot air from radiator, with less efficacy, not necessarily less power consumption. You could access 'An experimental investigation of NACA submerged Air Inlets on a 1/5 scale model of a fighter airplane', Donald E Gault, NACA RM Nº A7I06. Blessings +


text:
Who performs repossessions of airplanes?
When the owner of an aircraft defaults on their loan, their lender can send repo men to take the aircraft back, often against the owner’s will. However, unlike cars, which can be driven by anyone with a license, there are so many expensive type ratings for aircraft.
Do they specifically hire a pilot with the needed rating for each given job, or are there dedicate aviation repo men with scores of type ratings to cover any eventuality? It seems like the skill set to fly the plane doesn’t necessarily qualify you to slip in quietly and take it back from a belligerent owner.
Also, my friend Bianfable got me thinking of another issue. Who repossesses aircraft when the owner has fled with it to a foreign country?

This sounds pretty country specific. Could you add a country tag?

@Bianfable: Is it? That’s surprising. I know type ratings are required by many agencies across many countries, and I assume that aircraft buyers stop paying their loans all over the world. I don’t see how it’s relevant to say “Oh by the way... I’m from the U.S.” Why not just tell me how they handle it over in Germany?

Sure, type ratings are required everywhere, but who performs repossessions obviously varies by country. In Germany, that would probably be a court representative (Gerichtsvollzieher), who is unlikely to have a pilot licence. I don't know how they would actually perform the repossession...

@Bianfable: Perhaps you could look into it. Then you would know who actually performs the repossessions. If that isn’t something that interests you, then maybe there are other questions on this site that are more to your liking.

Yes there are a couple of reality TV shows that have been done on repos.  There are companies who specialize in the business, and the pilots have to be type rated where appropriate.  They have to be legal to fly the airplane.
It takes a special kind of risk taker pilot to do that kind of work, in view of the risks of getting into confrontations with irate owners, and flying airplanes that may or may not be airworthy.  The companies are usually hired by the holder of the chattel mortgage on the aircraft; the lender in other words (and who is, ultimately, the owner).  Banks and leasing companies generally, and even government foreign aid financing organizations from time to time.
Yes the scenarios presented on the tv shows are semi-fictional BS,  with dopey staged chase scenes, but even dialing the drama back closer to reality, it's not a job for the faint of heart.

"flying airplanes that may or may not be airworthy" -- the pilot does not have the right to break airworthiness law. If it isn't airworthy, it can't be flown.

“Airplane Repo” and other reality TV shows about aircraft repossession are as fake as a $3 bill.  Yes, some of the principle characters are real and perform repossessions but the whole thing is pure fictional drama (Yeah, you’re doing a takeoff roll in a Lear 35 as irate owners chase you and it just happens to have a GoPro mounted on the belly.)

@CarloFelicione: I’ve never seen any of the shows, and I don’t know about the cameras, but just a few days ago, I saw an irate owner speed across the grass, taxiways, and runway of an airport in his Cadillac, trying to stop the repossession of his Robinson helicopter. He was banging on the side of the door as the repo pilot was performing startup procedures. A few minutes later, a police car raced over to get the situation under control. The pissed-off owner was yelling, waving his hands, and kicking the ground as he watched his R44 flying away. That’s what made me curious about this topic.

@CarloFelicione of course it's overdramatized bs but there are repo men doing airplanes and they have to get around  owners who may not want to be repo'ed, like with cars.  And the airplanes they fly, they know little about.  It's not a job for the feint of heart.

Having witnessed the repo of lower cost planes, as well as exec jets, usually the team shows up, and the mechanic and pilot (for larger aircraft) seek to get keys, logbooks, etc. and there is often a lead who works with the owner, FBO, mechanic who normally services the aircraft.  From my observation it is a negotiated departure.

Yes probably 90% of the time, and especially within the US.  Going out of country can become a bit more problematic.


text:
What advantages are there to operate a corporate flight department under Part 135 as a separate entity instead of in-house as a Part 91?
This question specifically involves FAA regulations in the U.S.
Some U.S. corporate flight departments will set up a separate business entity for their flight operations to limit the liability of the parent company. Because this business operates with on-demand passenger transport for compensation as its primary business, it must be operated as a part 135 (or 125 if they are running big ships) instead of part 91. In some cases, this new subsidiary will provide additional revenue stream by servicing outside clientele in addition to meeting the travel needs of its parent company, and sometimes they remain exclusive.
If a corporate flight department doesn’t want to use their aircraft to supplement income with charter flights, is liability the only reason to set up and operate as a Part 135 instead of keeping it Part 91?
Are there any other reasons, aside from liability and supplemental income, to bother with a 135?

If a company's needs are such that they don't need an aircraft on call 24/7, I think most will do fractional ownership shares instead of renting out.

I don't know if anyone here can answer your question well. Liability isn't a simple, well-defined thing and there could also be insurance and tax implications that play into a decision. An aviation lawyer and an accountant for your jurisdiction could give you better advice than we can.

@Pondlife: You may be right. I just thought someone on here might have some firsthand corporate experience who could point out some details that I may be missing.

“better” is opinion-based. Asking for factors to consider, so you can make up your own mind, isn’t.

@StephenS: That’s patently ridiculous. There are billions of examples of things that are “objectively better” than others. I am asking if there are objective advantages of one over the other.

@AaronHolmes It was a helpful suggestion to avoid getting your question closed (there’s already one vote, not me), and it seems a minor rephrasing to match what you are actually asking anyway.

@StephenS I fully agree. I took the liberty of making the changes. Aaron Holmes, feel free to edit again if I inadvertently changed the meaning of the question.

@Bianfable: I see the source of possible confusion and have added some information to make it more clear. Nevertheless, there is a fundamental dislike of the word “better” on this site, as if it always denotes subjective opinion. There are myriad ways to objectively show that one thing is better than another. If two aircraft, being essentially equal in their performance and design characteristics, have a dramatic difference between their max operating range, it is ok to say that the longer range model is objectively better. Is it better to compete in a football match barefoot or with cleats?

@AaronHolmes I agree that the word "better" in the question does not justify closing it as opinion-based (and I didn't vote to close it). Nonetheless, the initial version of this question was borderline opinion-based because it was essentially asking about a business decision, where "better" depends on a lot of things like: is it better financially (cheaper), is it legally riskier, is it more flexible, etc. In the end, most business decisions are quite subjective.

There is no reason you can't operate as a part 91 department but simply adopt the standards of 135.  Government contracts work this way.  It's all pt91 work but adheres to pt135 rules.
Actually holding a 135 is a lot of work and is expensive.  The training and checking requirements are onerous for your average flight department.  How do you feel about potential career limiting checkrides every six months?  You also need to keep the planes up to a higher standard.  This means observing TBO hours and calendar times.
You don't mention aircraft types, but Continental requires piston engine overhauls at 12 year intervals or upon reaching the time limit, whichever is first.  Even a piston single becomes expensive to operate.


text:
CH-37 Mojave Helicopter decibels
What was the decibels level for the Sikorsky CH-37 Mojave Helicopter?   1956 --1959. I need this information for the VA, to process my hearing claim. I was a crew chief in the Army.

Sounds levels change with distance, what was your proximity?

Quite a few former crew members here experience the similar hearing problems and same treatment by VA.

Although that specific information may be impossible to get without starting up a Mojave and standing underneath with a sound level meter, it is generally understood that helicopter noise can easily exceed 100db. The CDC indicates that permanent hearing loss can occur after 15 minutes of exposure to this level of sound.
Here is a link to a study on helicopter decibel levels.
Here is a link to the CDC page on hearing loss.
Here is a link to a Purdue University chart, listing a Bell helicopter’s sound level at 100db flying 100 feet overhead.
I hope this helps at the VA. Thank you for your service.

While this is a good answer, links rot, so it is customary to quote the relevant portions of a linked document in the answer itself.

Noise level of one installation can only be used make rough estimates for noise levels on other installations. Decibel is a very tricky unit, and keeping in mind the complexity of acoustics, I would not use engine noise in this aircraft to present the noise level of the same engine type on that aircraft.

Direct quotes are not necessary as the only relevant data - 100db sound level and its negative effect on hearing - has been included.

Engine noise is only one component of noise when it comes to helicopters. Engines, main rotors and anti-torque systems each add to the total sound level in separate Hz ranges.


text:
What is the distance between RLLS lights?
I've looked everywhere for a few days now, but I can't seem to find the distance between lights on an RLLS approach lighting system. The specific one I am looking at is for the 31C approach at KMDW.

Approach Lighting Systems (ALS) can have many variations, but each variation will be a combination of certain components.
For example, green runway threshold lights extend across the runway threshold, 5 feet apart (center-to-center), and extend outward 45 feet from the runway’s edge on either side. This line of lights can be up to 10 feet from the landing surface before requiring a waiver.

Centerline lights are rows of 5 lights that span 13.5 feet wide and are usually spaced 100 feet apart extending away from the runway threshold out as far as 3,000 feet in some cases.

Many other lights may be incorporated, including sequenced flashers, runway alignment indicators (RAILS), side row bars, and wing bars.
In general, rows of lights will usually be 100 feet apart for at least the last 1,000 feet, and 200 feet apart beyond that.

For more detail on all of the various types of lighting and specific measurements between each, check out this article on Code 7700.


text:
How do I simplify explanations for the drag formula?
With reference to aircraft aerodynamics:

As the aircraft speed increases the aerodynamic load increases in a
mathematical relationship proportional to the air density and the square of
velocity.

What does the above statement mean in layman's terms? Consider explaining it to a high school student.
Also, what's the simplest explanation for the drag formula too?

Fd=1/2 *Density *Velocity^2 *Coeff. drag *Area

First, make it relatable.  (See my answer to aileron effectiveness question)  After the basic concept is clear then you can delve into the underlying equations that help us quantify the phenomenon.

Trying a less mathematical way to make the equation plausible:
$D = q \times A_{ref}\times c_D $
(with $q = \frac{\rho}{2}v^2$)
$q$ is the so-called "dynamic pressure". That's the increase in pressure you get from stopping the air coming towards your airplane (or car, or whatever) down. As long as you're not getting close to the speed of sound, that's the pressure increase you get at the tip of your aircraft. That air is trying to slow your aircraft down because that air wanted to just go on as it did but you just pushed an aircraft in its face.
This pressure doubles as the air density doubles (because there's more mass of air being pushed around), but it quadruples as velocity doubles (because that air is being slowed down a lot harder if it's faster -- the square comes out of the kinetic energy equation).
Now, pressure is force per area. The bigger your aircraft, the more of it you'll get. So if you're multiplying it by your reference area, you get the force that would push you back if that dynamic pressure was acting on your whole reference area. A cube moving straight through air with one of its faces in front is relatively close to generating that much drag.
But of course a decent aircraft is a little better than a cube. It's trying to slip through with as little disturbance as it can, and that's why a good aircraft has a low drag coefficient. So the drag coefficient effectively tells us how much drag the aircraft produces compared to (roughly) a cube moving straight through the air, where one face is as big as $A_{ref}$. For a passenger aircraft these days, $c_D$ is somewhere from 0.02 to 0.03 during cruise.
$D = q \times A_{ref}\times c_D $
$D \approx D_{cube} \times c_D $
The nice thing about this:
$c_D$ is independent of speed, density or size -- it's just a function of the aircaft shape. So if you build a wind tunnel model (which is smaller) and put it in a wind tunnel (which is slower than the real flight), your $c_D$ is mostly the same as for a real aircraft (ignoring Reynolds number effects, they're for another day).
Two things to remember:
1: The reference area is not some fundamental number. For a sphere or a cube, people take the cross-section area, for a car, it's usually the frontal area (i.e. the size of the shadow if you shine a lamp at it from very far ahead, against a wall), and for airplanes people usually use the wing planform area -- but there are slightly different ways of defining that. That's not a problem though, as long as you remember which area was used for the $c_D$ you're working with.
2: For an aircraft in particular, $c_D$ is not constant, because it depends on $c_L$ (the lift coefficient). For a car, that's much easier because it is mostly constant.

As the aircraft speed increases the aerodynamic load increases in a mathematical relationship proportional to the air density and the square of velocity.

What does the above statement mean in layman's terms?

When a body (here an aircraft) is moving, an airflow is created surrounding the aircraft. This leads to aerodynamics forces which are forces acted by air on the aircraft body. It is common and useful to separate it into different components: Drag (opposite to movement) and Lift (perpendicular to movement).

Your statement mean: theses forces become more and more strong when flow speed and gas density increase. To understand this, you can write Newton's second Law (which you have/will probably study in high school) :

$$ \sum\vec{F} = m\vec{a} $$

As you see, a force is linked to the mass of the fluid or solid considered. If the density (mass per unit of volume) increase, the mass of air inside a same volume is raising too, as well as aerodynamics loads. To find the square velocity you need to manipulate differential (which you may not study during high school) but you can think about kinetic energy of the flow, which is the energy due to air motion (more that energy is high and more aerodynamics forces will be):

$$E_k = \tfrac{1}{2}mV^2$$

Also, what's the simplest explanation for the drag formula too?

$F_D = \frac{1}{2} \rho V^2 A C_D$

This formula express Drag dependency with other fluid quantities. In fact, coefficient $C_D$ comes from dimensional analysis. The goal is to find a metric (without dimension) to evaluate and analysis drag between different shape, body, airfoils, settings, etc..

Note
Even if you have $\rho$ and $V^2$ in this formula, this does not mean that the drag $F_D$ varying in the same way that these quantities. Indeed, coefficient $C_D$ is dependent of other non dimensional parameters such as $R_e$ (Reynolds number), $\alpha_i$ (angle of attack of fluid), etc

 An increase in velocity $V$ will affect $V^2$ but can also lead to a different value of $C_D$..

I tied to popularized some concepts and hope these elements can help you (but I'm aware these can be quite technical for high school level).

Part 1:
As an aircraft travels faster, drag increases more in thicker air (usually lower to the ground) more than it does in thinner air (usually higher in the atmosphere).
Also, doubling speed quadruples drag.
Part 2:
Force of Drag (self-explanatory) =
Density (the thickness of air or how many molecules there are in a cubic meter) * Velocity^2 (the aircraft’s speed multiplied by its own value)
divide this value by 2
then multiply by Coefficient of Drag (basically, a value that shows how easily an object will slide through the air)
finally, multiply by Area (how much surface is actually in contact with the air. Obviously, a bigger object will interact with more air, increasing drag).
Hope this helps!

"how many molecules there are in a square meter" – should't that be a cubic meter?

@Peter Kämpf: Slip of the tongue, so to speak. Yes. Cubic meter is correct.

Double velocity = 4 times the drag is the most common sense

The explanation I would like to present is
We are surrrounded by Air Molecules which has a certain pressure exerted on us. Therefore when the aircraft moves forward there is a resistance which is stopping the motion aka air resistance. This is the drag which is the pressure exerted on the body to move forward. When this is overcame the aircraft moves forward.
When the aircraft speed increases the kinetic energy of the air molecules increases thereby increasing the pressure acting on the body which in turn increases the drag or the air resistance. Kinetic energy the velocity is squared thereby it can be understood.
Considering idea gas it can be seen that density is directly proportional to pressure . Therefore this pressure has an effect on force acting on the body with respect to area. Therefore if density is increased pressure increases and force(drag) increases.
PS : - Please correct me if i am wrong.

This is by far the best answer because it doesn't just "throw a bunch of equations" at the recipient. Unfortunately people often just start sprouting off equations rather than trying to explain the underlying effect like you have done. This shows a lot better understanding rather than just "the equation has a little 2 next to the v"!!!

This explanation assumes that the high school students know the concepts of kinetic energy and work
If we look at the kinetic energy of the air in front of the object, we note that:
$$ E = \frac{1}{2} \cdot m \cdot V^2 \tag{1} $$
If we assume that only the air within distance $ds$ times a frontal surface $S$ gets affected, we can write $m$ as:
$$ m = \rho \cdot ds \cdot S  \tag{2}$$
If we plug $(2)$ into $(1)$ to get:
$$E = \frac{1}{2} \cdot \rho \cdot ds \cdot S \cdot V^2 \tag{3}$$
We also know that work is equal to (dragging) force $[D]$ times distance:
$$ W = D \cdot ds \tag{4} $$
Due to the energy balance, the energy lost by the air $E$ is equal to the work $W$ done on the object :
$$W = E \tag{5}$$
We then subsitute $(4)$ for the left hand side and $(3)$ for the right hand side:
$$ D \cdot ds  =  \frac{1}{2} \cdot \rho \cdot ds \cdot S \cdot V^2  \tag{6} $$
And we can divide both left and right by $ds$ to obtain:
$$ D  =  \frac{1}{2} \cdot \rho  \cdot S \cdot V^2  \tag{7} $$
However, this assumes that all the energy contained within our air packet $m$ is completely transferred to the object. And the influence of the object is indeed limited to our air packet $m$ (with size $ds \times S$) . This is usually not the case, and to indicate to what degree this happens we add a correction factor $C_D$ to $(7)$:
$$ D = C_D \cdot \frac{1}{2} \cdot \rho \cdot S \cdot V^2 $$
This also gives you a nice bridge to explain more about the meaning $C_D$ and how it varies for different shapes.
In what situation will you have a $C_D$ of 1? What can you do to reduce $C_D$? What does it mean when $C_D$ is larger than 1?

Image from very useful Wikipedia page of Drag Coefficient

Not really agree with the statement “All the energy contained in the air is transferred to the object.” How energy could be transferred to the solid if it is still motionless and without heat transfert ? (First thermodynamics law) This is more likely that gas kinetic energy is changed in pressure form (energy conservation eq.) leading to aerodynamic forces like drag.

See the image, the case at the top, in the 'idealized' case all air completely stops, and all the kinetic energy is transferred to the plate through the drag force. This allows us to make the energy balance between kinetic energy and work. For the energy balance the intermediate steps don't matter. If you want to make the intermediate step to pressure it's possible, but it only complicates the derivation, and leads to the same result.

I agree with the formulas you gave, but not really the explanation (I know, I split hairs a little bit here). If the plate do not move, the object does not apply any work nor get some kinetic energy at all. For me, all energy transformation happens inside air flow itself..

@Acsed. there has to be a transfer to the object. How do you explain the transfer using pressure if there is no movement (in the end pressure is nothing more than force over surface, so the explanation is fundamentally not different)? Please feel free to post your version of the answer, so you have more space to explain.

« in the end pressure is nothing more than force over surface, so the explanation is fundamentally not different. » Indeed, at the end, we arrived to the same conclusion. I just noticed that applying force is different to transfer energy. By considering the object itself, it is not moving, therefore its kinetic energy is zero and no work could be done from it. On the other side, many things happened in the flow where kinetic energy is changed to pressure form.   Anyway, this is a nice debate (even if we need, as you said, more space to explain our views ;)

I don't see the distinction between applying force over a distance, and energy transfer. The object is not moving, but the air is moving over it, it experiences force over a distance, hence it's performing work. This work done means that energy is transferred.
If an object's speed is zero, that doesn't mean no work could be done on it.

Work is the product of force and displacement (wikipedia). If the object is not moving, then the point where aerodynamic forces are applied does not move, then displacement is zero and so work. But, I found an experiment that match your vision (by moving the plate inside a zero-speed gas which is driven by the object to reach the same velocity) which leads to the same conclusion. So I am sorry for this long but interesting conceptual debate.

@Acsed, can you provide resources of the experiment, sounds like an interesting read :)

Hum, it is just an experiment or an imaginary configuration in my mind (like we do in thermodynamics for instance). But it convince me that your vision could be equivalent.


text:
What are these blades on the engine cowling of a Wittman Tailwind?
The Florida Air Museum in Lakeland has a Wittman W-8 Tailwind with four wooden, propeller-like blades on the engine cowling:

Source: own work
What are the blades for? It's an experimental aircraft so it's possible that they're unique to this specific airframe.

That Tailwind has several unique features, including retractable landing gear, adjustable air inlets, and a cowl flap.  It was built by a guy named Anthony Occhipinti about 1966.  I've seen pictures of it in the past but not with the vanes. It definitely is a one-off.

I wonder if the vanes might be intended to serve as "flow straighteners" to reduce the spiral of the propwash-- possibly to increase efficiency and/or to eliminate thrust-related asymmetry in handling (i.e. need for right rudder at high power and low airspeed.)  You don't happen to have a picture from the other side to show whether the curved side is on the top or the bottom on those blades do you?  On the other hand, a close look suggests the blades are moveable, which may tend to go against this interpretation.

@quietflyer  I won't post it as an answer because I don't know for sure, but I am fairly certain that the owner was experimenting with ways to mitigate P factor and torque effects to gain a few knots.  I've been in EAA since the mid 70s and this sort of home brew experimentation was very common back when most homebuilts were made from scratch and individual builders would heavily customize their aircraft and try different things.

I suppose they are probably only ground-adjustable not movable in flight.  Sure would be interesting to see a photo from other side to see whether the 2 blades on the right were mounted with the more curved surface of the airfoil facing up or facing down; if were to straighten out the spiral slipstream one would tend to expect the latter.

@quietflyer I added another picture taken from directly in front. I don't have one of the other side specifically

It sure looks like right horizontal one is upside-down compared to the left horizontal one, consistent w/ straightening the slipstream.  Someone ought to  write an actual answer out of all this--

I honestly have no idea! This might take a long time until it becomes answered

After calling the Florida Air Museum, I have discovered that this seems to be a local mystery to the employees at the facility, as well. The museum’s director assumed that they “were an attempt to counteract P-factor or torque. Something to do with balancing required power.”
Since this was little help, I did some more digging and decided that the “blades” on this Wittman seemed to function as adjustable strakes - albeit located far from any control surface and of dubious utility.
Finally, I discovered that there have been numerous experiments performed with ‘Actuated Forebody Strakes’ aimed at controlling forebody vortices as a means of complementing thrust vectoring. Additionally, a NASA study found that a large increase in yawing moment may be brought about through the manipulation of actuated forebody strakes.
In every case that I could find, the tests were concerned with fighter jet aircraft operating at high angles of attack, but it is conceivable that the owner of this Wittman W-8 was attempting to implement some of the same advantages here.
Here are the abstracts to the vortex thrust vectoring and NASA yawing moment studies:

The desirability to enhance the controllability of fighter aircraft at high angles of attack, particularly yaw control, has fostered an interest in both vectored thrust and active control of forebody vortices... The methods investigated include pneumatic or blowing techniques using surface mounted jets and slots, surface suction, variable-height deployable strakes, and rotatable-tip strakes. Flow visualization, and force and moment measurements have shown that all of the methods are effective at manipulating the forebody vortices over a wide range of angles-of-attack and sideslip, primarily through control over flow separation on the surface of the forebody. All are most effective when applied near the forebody tip.

Extensive pressure measurements and off-surface flow visualization were obtained on the forebody and strakes of the NASA F-18 High Alpha Research Vehicle (HARV) equipped with actuated forebody strakes. Forebody yawing moments were obtained by integrating the circumferential pressures on the forebody and strakes. Results show that large yawing moments can be generated with forebody strakes. At angles of attack greater than 40°, deflecting one strake at a time resulted in a forebody yawing moment control reversal for small strake deflection angles. At α = 40° and 50°, deflecting the strakes differentially about a 20° symmetric strake deployment eliminated the control reversal and produced a near linear variation of forebody yawing moment with differential strake deflection. At α = 50° and for 0° and 20° symmetric strake deployments, a larger forebody yawing moment was generated by the forward fuselage (between the radome and the apex of the leading-edge extensions), than on the radome where the actuated forebody strakes were located.

References:
Malcolm, G., & Ng, T. (1990). Forebody Vortex Control as a Complement to Thrust Vectoring. SAE Transactions, 99, 1515-1543. Retrieved August 16, 2020, from Journal of Aerospace
Fischer, D.F., Muriel, D.G., & Lanser, W.R. (1996). Effect of actuated forebody strakes on the forebody aerodynamics of the NASA F-18 HARV. NASA Technical Memorandum 4774. Retrieved from NASA.gov

Fantastic research, thanks!


text:
Can an airfoil have multiple aerodynamic centers?
Aerodynamic center is a point where the moment is independent of angle of attack. Can we have 2 or more such points? Does it necessarily lie inside the airfoil?

No, it's not possible to have them simultaneously. Here's a proof by contradiction:
Assume that there are two points on the airfoil that have constant pitching moment, located at $x_0$ and $x_1$, each having constant moments $M_0$ and $M_1$, respectively, and that $\frac{\partial{M_0}}{{\partial\alpha}}=\frac{\partial{M_1}}{{\partial\alpha}}=0$ (which make them aerodynamic centres).
Therefore, using the $M_0$, we can write the moment about any other point as:
$$M(x)=M_0 + L(x-x_0) \tag{1}$$
where $L$ is lift and is a function of the AOA, $\alpha$.
Using (1), we can try to calculate the moment at $x_1$, which gives:
$$M_1 = M(x_1)=M_0+L(x_1-x_0) \tag{2}$$
Differentiate (2) with respect to $\alpha$, and we get:
$$\frac{\partial M_1}{\partial \alpha} = \frac{\partial L}{\partial \alpha}(x_1 - x_0) \tag{3}$$
But (3) can't be zero since $\frac{\partial L}{\partial \alpha}$ is always non-zero, which contradicts with the assumption that $\frac{\partial M_1}{\partial \alpha}=0$.
However, if the lift is non-linear, then the AC will move around at different AOAs, each satisfying local linearity of the aerodynamic center definition.

Actually, there is one for subsonic flow and one for supersonic flow, with a complicated transition at transsonic speed. But not two at the same flow condition. +1


text:
Why does turbofan exhaust appear to reverse direction?
Yesterday I was at the airport planespotting. I observed the exhaust of a couple of turbofan engines, and found it curious how the fluid seemed to behave as it was leaving the engine and gaining distance to the aircraft.
From observation, this is what it appeared like:

The exhaust left the engine in a high speed, violent manner and quickly slowed down as it got farther from the engine.
The exhaust appeared to move in the other direction, aka going back towards the airplane before it met with new high-velocity exhaust gas and was violently mixed and pushed again further from the plane.

I remember the Saturn V's exhaust being pulled back into the flame duct right after engine start as the flame gained speed and the surrounding pressure dropped, and I was curious if something similar was happening with the turbofan?

Source of image: https://space.stackexchange.com/questions/26183/why-does-air-get-sucked-in-for-a-moment-before-engine-start

What you are describing is a characteristic of fluid dynamics known as eddies. As different portions of the fluid flow faster than others, the friction and surface adhesion between the two layers cause swirling of the fluid and reversal of the current, creating a turbulent flow region. It is this same principle that holds a ping pong ball stationary in a moving column of air.
For a simple overview, you can check out this wikipedia page:
https://en.wikipedia.org/wiki/Eddy_(fluid_dynamics)
For a more scholarly exposition, try this:
https://arc.aiaa.org/doi/abs/10.2514/2.1794?journalCode=aiaaj


text:
Can I charge for editing footage from a video that was taken during a flight as a private pilot in US?
I am a private pilot, and I went with one of my friends to a skydiving trip in a rented Cessna 172 that we split the cost on pro-rata.
I also used my video making equipment to record the duration of the flight.
He wants entire video now; I know that I may legally ask him to pay the $100 that is his pro-rata share, but can I charge him for my time spent editing and making that video as well?

Are you asking about regulations in the US, or another country?

I am asking about regulations in US.

You might get some other ideas/answers posting at Law SE...hard to kind of parse the legal question from the aviation part.

How is that an aviation question? This look like the programming in a boat kind of scenario. Voting for moving to law.SE

programming in a boat kind of scenario  Heh !

More seriously, as I understand it from you guys, private pilots are - basically - "not allowed to charge money".  SURELY it is a very bad idea, for the sake of a few dozen dollars, to even delve in to the issue "OK FAA, I honestly wasn't charging for piloting but I was charging for ..."  You know how solicitors say "Avoid even the impression of wrongdoing" about their own trade; this would seem to apply there.

@sahmad could you just give your friend him the raw, un-edited footage?

In summary of the comments, there is no consensus. Some are on the side of "it's fine if you ensure separation of videography and piloting" others are on the side of "no CPL, no money". In short @sahmad, speak to a lawyer not randomers of the internet lol

@sahmad When you do speak to a lawyer, please do answer this question with their response as I am sure we would all be interested to hear their opinion.

I'm assuming you didn't do the editing while you were sitting in the cockpit, flying the plane. Charge him whatever you want for your time sitting at home on the computer. It doesn't matter where the footage was filmed, if you're charging him to cut it up, edit it together, and render. Even an aerial photography company will itemize the charges and list digital editing services separately from the filming flight.
Just to be safe, though: Make sure he pays you separately for the pro rata cost-share of the flight. You don't want to take a lump sum and have to explain what part was for the flight and what part was for something else entirely.

Unless the PPL had a bona-fide reason to make the flight that didn't include taking pictures, he cannot collect a pro-rata share of the flight.  There are four things the FAA looks for when determining whether the flight is incidental or not.  That is one of them.

@wbeard52: I believe he mentioned that he and his buddy were on a skydiving trip together. The camera was there to capture the fun.

@wbeard52 Exactly. If this ever gets investigated, the two questions the FAA will be asking is whether the flight was solely to ferry the friend and whether the videography payments were a condition of the flight and/or a backdoor way to pay more than the pro rata share rather than a bona fide payment for services other than the flight.

"He wants entire video now; I know that I may legally ask him to pay the $100 that is his pro-rata share,"  This seems very wrong.  Surely as a private pilot you are ABSOLUTELY not allowed to charge money for aerial photography - right?  OP seems to be conflating the idea "I can take 1/2 the costs from friends on flights", with, "I can run any flight business I want .. so long as I only take half!!".   Note that the editing issue is confusing and totally unrelated.

@Fattie: This sounds like a comment that should go on the original question, since it’s ultimately the pilot that can clarify what he means. The way I understood it was this: Dude takes buddy on a skydiving trip. Dude rents a plane for the trip, and splits cost with his friend. He brings along a go-pro to record the fun. Now back home, dude’s friend wants all the highlight footage from their trip, but there’s hours of stuff. So he wants to charge his friend for cutting and editing a highlight reel of their awesome adventure.

I am not a lawyer, so do not regard the following as legal advice, it is a suggestion only. Particularly since your Pilots Licence is involved, talk to a real lawyer.
As a friend who has a private pilots licence, PPL, you are indeed not allowed to charge for your services as a pilot; you are not a qualified commercial pilot, so cannot charge a commercial fee. It is then up to your friend to make the decision as to whether they want to take the risk of flying with a less qualified pilot. If they do, you can ask your friends to pay their share of the flight costs. Put this contribution request on its own in an email from your personal email address - such as sahmad@example.com - to your friend so that there is a written, timestamped record.
Separately, as a professional Videographer, you are perfectly within your rights to charge a commercial fee for the rental of your equipment and for your professional services such as video editing. This too comes with its own risks, as you are telling your client that you are qualified to do the job on a commercial basis; if you mess it up, they have every right to sue you for damages. Send your client (who in this case also (by sheer "coincidence") happens to be your friend), an itemised invoice by email from your professional email address - such as sahmadvideographyservices@example.com - to request that fee. This ensures that there is, again, a timestamped record of communication, and doing so from your separate, professional email address mitigates the risk of ambiguity.
Example
Let's take a look at a look at a fictional example to further explain why I feel that you would be allowed to charge for your Videography services. I have used £ to represent any currency.

One day, three legally unconnected people called A, B and C, decided to go for a flight in a Cessna 172. A was the aviator; they had worked hard to get their PPL and were happy to take friends flying. B was the brave one; today they would be jumping out of a perfectly viable aircraft in the name of YouTube views. C was the camera person, so as a professional Videographer, film making was their job. They had been doing it for many years and, having developed some expertise, deserved the respect of being paid at least the going rate that other Videographers were charging. B had met A and C on the street, so the three separate people had no prior relationship of any kind.
Before the flight, they took some time to get to know each-other in the airfield cafe (it was a posh airfield) and discuss the flight arrangements. A told B and C that the total price of the flight was going to cost £x and asked if they would each be happy to contribute £x/3 of that cost. B and C were both happy to do so.
C then turned to B. C said that their company, "C Movies Inc", charges £x/hour for film making, which consists of £y/hour for equipment hire and £z/hour for professional services such as camera operation and video editing. B agreed to pay this fee.
After the flight, A sent B and C an email to remind them that they had agreed to contribute £x/3 toward the cost of the flight. Both B and C sent their share to A, thanking A for a great day.
"C Movies Inc" also sent their invoice to B for services rendered. As discussed, this professional invoice showed how much "C Movies Inc" was charging for equipment hire, as well as for the professional services that C provided as a consultant of "C Movies Inc". B paid this invoice quickly and without question (clearly fictitious!)
B was then able to obtain many more likes, shares and subs. All their viewers were impressed that B had done something so crazy as to jump out of a plane that was not even about to crash at all.

What you are doing here is "wearing the hat" of both A and C, which legally is doable. They are clearly distinct hats, but you can wear them simultaneously. We all wear many figurative hats throughout our lives, so the law recognises that distinction.
In this example, though it was C who physically sent the invoice, legally they did so for and on behalf of "C Movies Inc", so it was actually "C Movies Inc" that sent the invoice. The formation of a company (LLC, LTD etc) creates a legal person in its own right, thereby creating another level of separation which further removes ambiguity. This means that while Sahmad (the natural person) cannot personally cannot charge for your pilot services, "Sahmad Videography Services Inc" (the company) can charge for its professional videography services.
My other point with this example is that if it were another person in the aircraft doing the Videography, then there would be no question. They would be able to charge for their services; end of discussion. The fact that you are that person should not cause any confusion if you communicate as described.
Unrelated Example
In Britain, you are not allowed to sell alcohol in a building that does not have an alcohol licence. You are, however allowed to give alcohol away for free. Separately, you can ask your visitors for donations, or to buy something non-alcoholic. For example, I have heard of some organisations charging their event attendees £5 for a raffle ticket, and each ticket comes with a free beer.
TL;DR
As long as you ensure clear separation and agree everything ahead of time, you should be fine.
But trust me on the lawyer.

"charging their event attendees £5 for a raffle ticket, and each ticket comes with a free beer" sounds like something the police would take a very dim view of. The "and each ticket comes with" feels far to closely intertwined. (I'm sure it's happened, just not that it would have been a valid defence had they got caught)

I was not giving it as a what should be done, just that I have heard of it happening. I know that a charity can give away alcohol at an event and then separately encourage donations for the charity, however.

Yeah, the only way that would possibly be on the up-and-up is if the beer is actually just-plain-free free, "no purchase necessary", and they merely happen to offer you one of their free beers when you buy a ticket. But you could still get the same beer without buying a raffle ticket, just by asking for it. Otherwise, that's called selling beer.

Offtopic, but: (Note that charity "free gifts" have come under scrutiny in recent decades in the US, since they started being such a common feature of fund-raising drives. US tax rules say that for donations over around 55 US, a gift in return must be subtracted from the amount claimed as a charitable donation for tax purposes, unless the "token" gift cost under 11 US, is worth no more than 110 US or 2% of the donation (whichever's less), and bears the charity's logo or name. source.)

-1 Unless there is a reason for the PPl to make the flight other than for the video, it would still run afoul of the regulations.  The exchange of pro rata money is only a small part of the equation.

Are you a lawyer @wbeard52?

I have added an example to further explain my position. No substitute for a lawyer though.

@wbeard52, what meets your criteria for a "bona fide" reason for a private pilot to go flying?  Isn't having fun good enough?  Are we supposed to justify the reason each time in our logbooks?

@James Geddes, for a non-lawyer that was a very legalistic answer.  I thought these guys were friends?  I wouldn't treat my friends this way, I would just shake hands and swap a little cash.  Unless you don't trust your friend...

@MichaelHall I am a Charity Trustee so I did put my company law hat on a bit there just to explain the point about separation. In real life, everyone knows what the deal is so throwing a few bob at your mate is perfectly fine.

And separation is appropriate if you expect to be audited.  But, if you are intentionally creating a paper trail it needs to be tight.  If there is no requirement to create a record, my advise would be simply don't create a record.

Hence my strong suggestion for OP to speak with a real lawyer not us random internet people LOL

@MichaelHall.  If the intent of the flight is to just have fun.  Then go do it but be advised.  If the passenger sets the destination and the time the flight will take it becomes much more of a gray area.  The answer by Ryan Mortensen is what I use to determine such cases.  I also have an answer here:  https://aviation.stackexchange.com/questions/79960/does-the-faa-consider-flights-that-generate-content-for-profitable-youtube-chann

@wbeard52, both you and Ryan have provided excellent answers.  My point is that you can make a strong case that no private pilot ever NEEDS to fly anywhere.  Pilots go flying all the time for no other reason than fun.  Landing at a new airport, getting that $100 hamburger, simply sightseeing.  If you introduce a business need requirement to the decision making process you needlessly complicate matters.  A mutual decision to travel together and share expenses should suffice.

Just like in Ryan’s rental car example:  We clearly understand when a cost sharing car pool situation becomes an unlicensed taxi business, why is it any more difficult to discern the difference when aircraft are involved?  It shouldn’t be, yet people go round and round and round....

First, can I suggest not using the wording like "I took one of my friends to skydiving trip". It rings somewhat different tone from message of passenger being incidental to your own trip.
Second, as was correctly pointed out, whatever you choose to do on videographing front is a separate matter from exercising privileges of PPL. Can't comment on regs & licencing standards in that industry.

I don't agree with your first paragraph.  Isn't watching your friend jump out of an airplane a perfectly legitimate reason to go flying?  The problem is the circular logic needed to try to justify the pilot flying:  Do you attempt to separate them, i.e. the pilot had some totally different reason for flying that day, or do you establish that they had a common interest?  I think both are valid points, but I don't think it is necessary to have that discussion unless this becomes a semi permanent arrangement between them.

I didn't make a strong statement to disagree with. In any case you'd have to convince FAA, not me, that it is enough of a personal motive. We all understand that pilot's "reason" might be less than genuine personal need. Since OP was specifically concerned about grey area, I'd err on the side of caution, including choice of words & tone. It does matter when regs are pretty clear on intent. PIC "wanting to go for $100 burger, where pax coincidentally happened to tag along for jumping" sounds different from "friend wanted to skydive so i took him to airport because i wanted to see him do it".

I think you're in a grey area based on it being your video and your equipment.
AC 120-12A contains the definition of being a carrier.

As long as you didn't do something like make a Facebook post seeking people to go flying with you I think it's safe to say you didn't hold out.

If you split the cost of the plane pro-rata then you didn't do it for compensation.

A video editing service is not directly related to flight operations.
To give an analogy: if your friend were driving a rental car that you split the cost on while you all went on vacation somewhere and you took some videos while he was driving, and after your vacation was over, you hired him to edit the videos you took, that would not make him be a taxi driver any more than it makes you an air carrier doing the same thing in a plane.
However, I noticed one fine detail:
"I also used my video making equipment to record the duration of the flight."
If he took the video using his equipment I think this would be black and white legal.
If you took the video and used your own equipment that could be viewed as you creating aerial video content and then profiting from it.  So I think this is a grey area.  However, the video editing itself would be okay.  I think the question would be who created the content? and did they make money on the content?

Not a lawyer but: should the OP offer his friend an unedited copy of the video for free?

I don't see why he can't give it for free. He just has to make sure he can't be accused of selling it. It's one of those things where it will be whatever the FAA says it is.

He wasn’t contracted to make the video. It was personal footage. It was taken entirely apart from any previous agreement. If his friend hadn’t brought it up again, it would’ve been his own personal property. Anyone asking why he can’t just give it to his friend for free obviously hasn’t spent any time cutting and editing from hours of stock footage.

Okay so I have no idea about the US laws - but let me approach it from another angle...
If it's a friend, why not give him the video and let him edit it?
Now if he's an annoying friend who never wants to pay stuff and with whom you have issues - which i guess is why you might be asking this question in the first place, if it's your footage filmed for your own self with your own equipment - with no intent to give it to him when you filmed it... then you are entirely entitled not to give him anything...
I'm also thinking what kind of friend would that be if in selling the material to him you might risk your license... if there's a risk of him reporting you, then that's not a friend and just tell him to sod off you're not giving him anything... if you see what i mean...

I'm not sure why there was a downvote, but I like this answer.


text:
Electrically heated windshields are mostly transparent, but their colors vary from light blue, yellow or light pink. Please explain
Found it on a quiz worded this way. No other details unfortunately. I can only assume it has to do with the heated element materials of tungsten or molybdenum reaction with film layer materials. Perhaps it is a coating to reflect nothing but infrared. Hope to explain to students taking aviation maintenance course on ice and rain systems.

Welcome to the site. If they are transparent how could they have a color? Please edit and add more detail.

This is borderline off-topic for me as it isn't clear what's being asked from the way it is worded. It would improve your question if you edited to explain the source of the quiz and explain you don't know what it means, otherwise I could see it getting closed.

It's not a problem, what was the quiz from, online or a magazine?

We found it in a folder of quizzes for this system. Do not know it's origin.

Well, fundamentally, different density materials refract light differently.  So it can be loosely explained at a high level by prisms, rainbows, etc.  In other words, Junior High level science.  What are your expectations for an acceptable answer?

The elements you added in the comment should be put into the question as they help understand. As @GdD suggest, knowing where the question comes from helps understand the expected understanding and knowledge before reading the question and thus it helps adapt answers without writing an entire book chapter.

The heating element in cockpit windows is typically a thin film comprised of a transparent conducting oxide - indium tin oxide is common. In thin layers, it is transparent to the visible light spectrum but acts as a mirror in the infrared. As with all transparent conductive films, there will be some  tradeoff between transparency and conductivity.
Thin-film interference is a natural phenomenon in which light waves reflected by the upper and lower boundaries of a thin film interfere with one another, either enhancing or reducing the reflected light. When the thickness of the film is an odd multiple of one quarter-wavelength of the light on it, the reflected waves from both surfaces interfere to cancel each other. Since the wave cannot be reflected, it is completely transmitted instead. Thus when white light, which consists of a range of wavelengths, is incident on the film, certain colors are intensified while others are attenuated. Thin-film interference explains the multiple colors seen in light reflected from soap bubbles and oil films on water. It is also the mechanism behind the action of antireflection coatings used on glasses and camera lenses.
For any certain thickness, the color will shift from a shorter to a longer wavelength as the angle changes from normal to oblique. This interference produces narrow reflection/transmission bandwidths, so the observed colors are rarely separate wavelengths, such as produced by a diffraction grating or prism, but a mixture of various wavelengths absent of others in the spectrum. Therefore, the colors observed are rarely those of the rainbow, but browns, golds, turquoises, teals, bright blues, purples, and magentas.
Additionally, keep in mind that in its thicker, bulk state, indium tin oxide is naturally yellowish-grey. Therefore, the thicker the film, the more it's natural color will influence the light passing through it. I don't know the natural colors for every transparent conductive film material, but it stands to reason that there will be some variation in natural coloration there as well, owing to the different elements included in the composite.

In cars, there are (rather older) examples of window heaters that are thin wires and not a conductive layer. Are these used in aviation?

@fraxinus: Yes. They have seen some use. For example, certain DC aircraft incorporated embedded wiring in their windows. The problem is visibility. For the same reason that cars dont use wires all across the front windscreen, this type of heating element obstructs a pilot's vision. Further, the uneven nature of the heating produced by this kind of system can cause additional optical distortion.


text:
What is the correct way to get established on the outbound track on this approach?

If you have been cleared to LCA (from the direction shown by the red arrow) then outbound on the procedure, what is correct way to get established on the outbound track?
Ideally, I'm looking for an ICAO/PANS-OPS reference or similar (not US).
Many thanks!
---- Edited for clarity ----
So, to avoid a situation like this:

What is the correct action to take?
Is it to request the arrival pattern hold to better align yourself:

Or manoeuvring space to the south to better align yourself:

Or something else?

Realistically, if approaching from the east, you would probably fly the ILS/VOR Y via AMAKO (https://i.imgur.com/PPyQrWR.png) or the ILS/VOR S via SOBOS (https://i.imgur.com/qk1cFlY.png). Still a valid and interesting question for theoretical purposes.

Related: How should one fly the entry procedure to an approach when the hold is not aligned with the outbound course?

Intersections include obstacle clearance for wide turns in your first example, some of these limit turns to less than 120degrees. It is expected to turn early to avoid going far beyond the intersection, this requires some extra navigation to estimate the start of the turn; dme, gpss, or another VOR. At 210kts a standard rate turn has a 1.1NM radius, so start 90 degree turn about 1.1NM before the intersection. 120deg 2.0NM and 135deg 2.7NM. At half the speed it is half the radius. I might also favor the south side of the inbound course for extra margin.

This turn angle is large enough that I would consider a left turn, or request hold pattern if in cat C or D. A continuous left turn to 025 [to intercept R053 or R062] is not holding, you would make use of the holding obstacle-clearance area but you would not request a hold. Your inbound course overlaps with the hold area anyway so ATC can not use the hold at your altitude in any case.

Just curious, why are you trying to avoid the first example?

@MichaelHall, probably because manoeuvring side is the south-east side so overshooting to the north-west is not guaranteed to be safe.

@Jan Hudec, the obstructions to the NW are just a bit higher that TPA, and (if to scale) approximately 6 miles away.  I don't know what ICAO says, but option one would be the standard in the US.  Unless an alternate was published due to terrain.  And if you are going to bother to key the mic to ask for anything else, why not just get vectors to a left base?

@MichaelHall, well, http://www.aviationchief.com/course-reversals.html suggests that it is not permitted under ICAO rules.

@Jan Hudec, that looks like an answer to me...

I do not have a specific ICAO reference. By my interpretation of the chart, you can approach the airport at any assigned altitude above 2300 feet MSL from your specified East direction. Just as long as your aircraft stays between the 71° radial clockwise to the 215° radial of the VOR. But, you would have to be above 4900 MSL to intercept any part of the instrument approach. Once you are established on the approach, you can drop down to the appropriate designated at-or-above altitude marked on the approach. If you are joining the approach at the LCA VOR, you would enter the hold, either climbing or descending until you reach an altitude where you can safely descend down to 1500 feet MSL during the teardrop course reversal. Remember, you have to remain at or above 4000 feet MSL until passing the VOR when leaving the hold. This will be your Minimum Holding Altitude as well as your Minimum Crossing Altitude at the LCA VOR.
If you have already been cleared for the procedure at LCA, you would just have to make your radio call once you reach the VOR for the hold, and again at the VOR when you leave the hold (if one is necessary to gain/lose altitude).

To answer the specific question: When arriving in the direction of the red arrow, enter the hold at LCA by flying a parallel entry.

@Gerry - You are correct about the recommended but not required entry into the hold being a parallel one. But, was the original question about the correct method to enter the hold? I read it as how do aircraft join the procedure. After all, if a Cat A or B aircraft’s heading were Northwest instead of West, no hold would be necessary nor advised. The hold is simply a convenient way to adjust altitude and avoid sharp turns. The hold is not an obligatory part of the procedure. It is strictly optional. Hence the thin vs thick lines.

Thanks for the reply! I've edited the original question to clarify what I'm asking

For the clearance described by the red arrow, believe you me, ATC expects you to make a maneuver exactly mimicking a parallel entry to the published LCA hold as depicted on the plate and thereafter proceed outbound on LCA R053 on returning to the VOR and continue with the teardrop/base turn Instrument Approach. Here's the official word on this (thanks ICAO, Jepp), as we all understand a pilot's trepidation at performing such a complex maneuver without much by way of a clearance. An appropriate R/T call "approaching overhead LCA, proceeding to turn left HDG 221" should do the trick. For extra safety, add "as per procedure". If this sounds too iffy, have agreement with ATC earlier.

As long as from the 1st passage of LCA, IAS < 210 and Altitude at or above 4000ft and the published holding inbound course is followed you are in the protected area of the published hold. There is no overt need for turn-anticipation, though it would be nice, and you can turn left to 221deg immediately on arriving overhead LCA.
Your 2nd option can work too if ATC is agreeable. I know it was legal and there was a published procedure in Australia to make a course alteration to facilitate a passage direct outbound for approach, it didn't require ATC "permission" as long as you were within the LSALT 25 mile circle and above LSALT. Can't imagine the busy airports of today allowing this except at times of very low traffic. In the airline cockpit it would require good anticipation of turns and proper orientation, and a suitable brief, an art that is slowly being lost.
Concepts discussed in the role of enthusiasts and answers given in good faith. They are not meant for any sort of implementation. Please consult current and officially provided documentation before operational use of any of the concepts discussed.
(write ups and diagrams courtesy ICAO/Jeppessen)

For a category A or B aircraft, with permission, 3rd diagram seems the most practical and safest.  A 45 degree into the holding pattern at 4000 feet (approaching from the East) also seemed good, unless faster, heavier traffic was also there.
First diagram would intersect 221, potentially near a high go-around.  Flying northwest of the airport might also have controllers freaking out a bit too.  Second diagram hopefully does not mean flying in the opposite direction of holding traffic.
Diagram three, slightly more to the southwest, may be the best choice for a light incoming aircraft approaching from 090.  Since the "missed approach" track is 155 to 335 at 2000 feet$^1$, 335 may be a useful entry to 053 downwind leg as per airport procedures.
More information shows aircraft in the holding pattern descend from 4000 feet to 1500 feet 8 miles from the 221 runway. A light aircraft in the "missed approach" entry at 2000 feet (around 3 miles from the southwest) could completely avoid holding pattern traffic (after flying the 053 downwind) until merging at the 1500 feet turn for the 221 final approach (as per diagram) or at any point before 8 miles out.
For a light aircraft with a final approach speed much lower than the category C and D aircraft flying the 062 downwind, this would present an option to further avoid traffic by turning base/final earlier than the 8 mile turn point.
In summary, larger/faster planes hold at 4000 feet for an 062 downwind.  Slower/lighter aircraft work the 053 downwind.  All are under ground control.
$^1$ Courtesy of @Dean F. more detailed diagram

Not a bad answer, but the OP is specifically asking for the "correct" way per ICAO, not the most practical, safest, best choice, or useful...  Your opinions are valid, but I believe they are just that - opinions.

Plain and simply ICAO DOC8168 says that max intercept angle for a base turn procedure is +/- 30 degrees to the outbound - just like it is 110 for an RNAV IAF, so if ATC is unaware of this (which they usually are) you request a heading to position better. Ask to do a track-reversal west of the beacon, or simply chance it and turn anticipate the hell out of it.

Definitely not west of the VOR, there is high ground there (MSA 7300). You either have to be vectored to arrive from the narrow heading range 23°–34° (or even narrower 33°–34° for cat C/D) or use the hold as published.